We propose to continue our ongoing work on the functional properties of the SV40 large T antigen (T), one of the two transforming proteins of the virus. Attention will be focused on the biological significance and the mechanism underlying the large T adenylation phenomenon. Moreover, we will attempt to develop tractable assays for the neoplastic transforming activity of purified T and, then, to use these to assay for this function in cells injected with various mutant and chemically modified wt T species. The major goal here is to understand the structure-function relationships underlying the large T transforming function. Finally, a parallel effort will be made to elucidate those key structure-function relationships which govern the in vitro biochemical activities of the protein. One of the purposes of this particular work is to begin to understand their physiologic significance and how they contribute to the in vivo behavior of this protein in both the lytic cycle and in SV40 transformed cells.